7.2 Converting a version 4 database

If you want to convert an existing version 4 database, the principal
conversion issue arises too.

If you decide to convert your database once and for all, you will only
have to do this conversion once. It is also possible to run a version 5
KDC as a slave to a version 4 KDC. In this case this conversion will
happen every time the database is propagated. When doing this
conversion, there are a few things to look out for. If you have stale
entries in the database, these entries will not be converted. This might
be because these principals are not used anymore, or it might be just
because the principal couldn't be converted.

You might also see problems with a many-to-one mapping of
principals. For instance, if you are using DNS lookups and you have two
principals `rcmd.foo' and `rcmd.bar', where `foo' is a CNAME
for `bar', the resulting principals will be the same. Since the
conversion function can't tell which is correct, these conflicts will
have to be resolved manually.

7.2.1 Conversion example

Given the following set of hosts and services:

foo.se rcmd
mail.foo.se rcmd, pop
ftp.bar.se rcmd, ftp

you have a database that consists of the following principals:

`rcmd.foo', `rcmd.mail', `pop.mail', `rcmd.ftp', and
`ftp.ftp'.

lets say you also got these extra principals: `rcmd.gone',
`rcmd.old-mail', where `gone.foo.se' was a machine that has
now passed away, and `old-mail.foo.se' was an old mail machine that
is now a CNAME for `mail.foo.se'.

When you convert this database you want the following conversions to be
done:

The `v4_name_convert' section says which names should be considered
having an instance consisting of a hostname, and it also says how the
names should be converted (for instance `rcmd' should be converted
to `host'). The `v4_instance_convert' section says how a
hostname should be qualified (this is just a hosts-file in
disguise). Host-instances that aren't covered by
`v4_instance_convert' are qualified by appending the contents of
the `default_domain'.

Actually, this example doesn't work. Or rather, it works to well. Since
it has no way of knowing which hostnames are valid and which are not, it
will happily convert `rcmd.gone' to `host/gone.foo.se'. This
isn't a big problem, but if you have run your kerberos realm for a few
years, chances are big that you have quite a few `junk' principals.

If you don't want this you can remove the `default_domain'
statement, but then you will have to add entries for all your hosts
in the `v4_instance_convert' section.

Instead of doing this you can use DNS to convert instances. This is not
a solution without problems, but it is probably easier than adding lots
of static host entries.

To enable DNS lookup you should turn on `v4_instance_resolve' in
the `[libdefaults]' section.

7.2.2 Converting a database

The database conversion is done with `hprop'. You can run this
command to propagate the database to the machine called
`slave-server' (which should be running a `hpropd').

hprop --source=krb4-db --master-key=/.m slave-server

This command can also be to use for converting the v4 database on the
server: